The major objective of this application is to develop a practical and highly effective post-exposure countermeasure to ricin. Ricin is a highly toxic protein produced by the castor bean plant. It is readily extracted from the beans with relatively little technical skill. Ricin is a potent toxin and it is estimated that less than a milligram is sufficient to kill a human. Given its widespread availability, high toxicity, and ease of extraction, ricin is viewed as a very probable terrorist threat. Consequently ricin has been classified as a Category B select agent by the Centers of Disease Control and Prevention (CDC). Currently, there is no approved therapy to treat ricin poisoning. The threat of a potential ricin attack is viewed as imminent and countermeasures must be found. Twinstrand Therapeutics Inc. (TTI) has invented and developed novel ways to convert ricin into non-toxic recombinant ricin toxoid. Twinstrand's lead molecule in oncology, TST10088, is currently being tested in clinical trials. This molecule, which in structure and immunogenicity is almost identical to ricin, provides the foundation to the development of a highly-effective antibody based ricin therapy. This project will focus on antibody-based therapies and will use a two-pronged approach: 1.) Fast-track of a horse-derived polyclonal antibody therapy and 2.) Develop the first fully human anti-ricin antibody therapy. In our first approach, horses will be immunized with recombinant TST10088 to elicit an anti-ricin immune response. Protocol and processes will be optimized to extract anti-ricin antibodies from horse plasma allowing us to stockpile ricin antidote. During the course of the equine antidote development, novel approaches will be investigated to test and improve the effectiveness of an antibody-based therapy to treat exposure to aerosolized ricin. An IND will be filed with the FDA within the first 2 years of this project and the antidote will be made available for emergency purposes. In our second approach, antibody-producing cells will be isolated from TST10088-immunized humans - patients who have already received TST10088 during the course of our phase I clinical trial. The mRNA/cDNA encoding anti-ricin antibodies will be extracted and cloned into mammalian expression libraries. Cells producing anti-ricin antibodies will be selected using high throughput screening technologies. Finally, fully human anti ricin antibodies will be produced in small-scale and characterized in vitro and in vivo.